Reliability

ReliabilityReliability

Chapter Ten

Reliability

DefinitionsDefinitions Reliability: The ability of a product, part,

or system to perform its intended function under a prescribed set of conditions

Failure: Situation in which a product, part, or system does not perform as intended

Normal operating conditions: The set of conditions under which an item’s reliability is specified

Reliability

Determine the reliability of the system shown

.98 .90

.90 .92

.95

Reliability ExampleReliability Example

Reliability

.98 .90+.90(1-.90) .95+.92(1-.95)

The system can be reduced to a series of three components

.98 x .99 x .996 = .966

SolutionSolution

Reliability

Few (random) failuresInfantmortality

Failures dueto wear-out

Time, T

Failure Rate CurveFailure Rate Curve

Reliability

Reliability = e -T/MTBF

1- e -T/MTBF

T Time

Failure Rate as an Failure Rate as an Exponential FunctionExponential Function

Reliability

Reliability

0 z

Normal ApproximationNormal Approximation

Reliability

AvailabilityAvailability The fraction of time a piece of equipment

is expected to be available for operation

AvailabilityMTBF

MTBF MTR

MTBF = mean time between failuresMTR = mean time to repair

Reliability

Improving ReliabilityImproving Reliability Component design Production/assembly techniques Testing Redundancy Preventive maintenance procedures User education System design